The use of dead bolts for security purposes is widespread. One example of a high security dead bolt lock is shown in U.S. Pat. No. 5,257,519 to Miller, the disclosure of which is incorporated herein by reference. Another example of these types of dead bolt mechanisms is shown in U.S. Pat. No. 4,601,504 to Wolfe, the disclosure of this patent also incorporated by reference herein. These dead bolt locks are combined with a safe lock for security purposes. The lock bolt of the safe lock provides the motive force to extend and retract the dead bolt of the dead bolt lock during operation. When using a combination type lock, a correct combination will permit retraction of the lock bolt. One drawback of such devices is that safe lock bolts and actuating mechanisms may not be well suited for long term use in this manner. In other words, they may not be designed to exert the necessary pushing or pulling force during extension and retraction of the dead bolt.
A dead bolt hold back feature has also been provided which retains the dead bolt in a retracted state. The dead bolt automatically extends as the door closes and a trigger member contacts the door strike. The extended dead bolt may be retracted from the inside of the secured area by rotation of a dead bolt knob. The aforementioned patents also disclose a life safety feature which retains the dead bolt in a retracted position so that a person inside a secured area can close the door without having the dead bolt extend. This feature enables quick exit from the secured area, however, it is not usually desirable to leave the door unlocked in this manner. On the other hand, when the life safety feature is not enabled, the above-mentioned dead bolt knobs do not provide a particularly easy manner of escape for individuals with various disabilities.
Often times, dead bolt locks on doors are combined with a second electric lock. The second lock often takes the form of an electronic access control linked to an electric door strike or lock associated with the door knob. Unlocking information provided to the access control actuates the door strike and, upon the additional retraction of any dead bolt, allows the door to be opened. It will be appreciated that this combination of a dead bolt lock and a doorknob lock makes it difficult to exit the secured area. A person leaving the secured area must use two hands to turn the doorknob and the dead bolt retraction knob simultaneously to open the door. Again, disabled individuals may have problems when trying to exit through such a door, particularly in the event of an emergency.
Further, many lock systems are vulnerable to opening through the application of shock loads, such as during an attempted unauthorized forced entry. For example, a shock load can cause a handle to rotate under its own weight potentially withdrawing a dead bolt and opening a door. Similarly, the application of a shock load can cause the dead bolt to move of its own initiative. For example, a heavy blow delivered to the dead bolt lock or door may cause the dead bolt, because of inertia, to retract into a retracted position in which the lock system is unlocked. Hence, the dead bolt lock is susceptible to unauthorized opening by a person familiar with their construction.
In view of these and other problems in this area of the lock industry, a need has developed to provide an improved dead bolt lock system.